This invention relates to a cellular polyurethane, the preparation thereof, and its use in packaging of fragile or delicate articles.
Fragile or delicate articles including, for example, electronic instruments, delicate glass, and shock sensitive chemicals require special protection if they are not to be damaged when transported or stored. A well-known practice is to employ a cellular, shock absorbing plastic packaging material, such as polystyrene or polyurethane foam, to encapsulate and support the article within the confines of a rigid or semirigid box or enclosure. Such techniques are disclosed in, for example, U.S. Pat. Nos. 2,897,641; 3,190,422; 3,173,535; 3,415,364 and 3,750,871. When polyurethane foam is selected as the packaging material, it is typically a rigid or semirigid polyurethane foam having a density of from about 8 to about 15 kilograms per cubic meter. While rigid or semirigid packaging foam functions to restrict the physical movement of the packaged article, it is frequently observed that its ability to attenuate impact shocks and vibrations does not always satisfy the demands of industry.
As an alternative, flexible or semi-flexible polyurethane foam, recognized as having better sound and vibration attenuation properties, may be considered for use in packaging applications. However, the load bearing characteristics of such foam does not always satisfy the demands of industry for the packaging of the sensitive articles. Accordingly it would be desirable to develop a polyurethane foam for use in packaging applications that can effectively attenuate impact shocks and vibrations and which has attractive load bearing properties. Further to improving such properties, it would also be desirable if such foam could exhibit an enhanced fatigue resistance. Foam having an enhanced fatigue resistance would allow it to be considered for reuse in the packaging application without it having to be immediately scrapped.
In addition to the above-mentioned desired performance requirements, it would be desirable if the polyurethane foam could be prepared by a process having none or little volatile emissions to the environment of substances considered as environmentally undesirable. Particularly, it would be desirable to avoid the use of certain halogenated blowing agents considered as being aggressive to the ozone content of the earths' atmosphere.